1. FIELD OF THE INVENTION
This invention relates to a clutch assembly capable of changing over transmission and nontransmission of a prime moving force selectively.
2. DESCRIPTION OF THE PRIOR ART
Conventionally, as a clutch assembly to selectively transmit a force of a driving source to a driven object, for example, an engaging clutch is known. For instance, the Japanese Unexamined Patent Publication No. 60-26821 published Feb. 9, 1985 discloses a clutch assembly capable of coupling a driving body to a driven body, by forming a plurality of engaging holes in the driving body, and retractably provided engaging shafts to be engaged with the engaging holes in the driven body, with the driving body and driven body being arranged on the same center line. In this clutch assembly, when transferring from a state of transmitting the driving force with the driving shafts and driven shafts being coupled together to a state of nontransmission, it is necessary to draw back the engaging shafts which are engaged with the engaging holes to be separated from the driving body. At this time, on the contact surface between the engaging holes and engaging shafts, there is a surface pressure P generated, corresponding to the shaft torque being transmitted (that is, the rotary load of the driven body). Supposing the coefficient of friction on the contact surface to be .mu., a force P.times..mu. is required to isolate the engaging shafts from the engaging holes. Therefore, a considerably large force is needed to separate while transmitting a large shaft torque. Accordingly, when the engaging shafts are moved forward and backward by a solenoid or the like, a very large solenoid is required. In addition, the reliability of action is inferior.